The invention relates to transmitting messages in a telecommunication system comprising a packet radio network.
In the GSM system, short message services SMS have turned out to be extremely popular. Short messages are used for text-based messaging between users or to convey application data, such as WAP (Wireless Application Protocol) application data. Short messages are relayed by a short message service center (SM-SC), which forwards short messages and stores and retransmits messages that have not been delivered. The SM-SC is able to receive a short message via any network for delivery to a mobile station MS. The SM-SC transfers a short message received to a gateway mobile switching center for short message service (SMS-GMSC) to be delivered further to a mobile station. A mobile-originating short message is relayed via an interworking mobile switching center for short message service (SMS-IWMSC) to the SM-SC to be delivered further. Signalling channels may be utilized in transmitting and receiving short messages; hence no separate traffic channel is required.
Short message services have turned out to be necessary also for the general packet radio service (GPRS) developed for the GSM system. The GPRS comprises serving GPRS support nodes (SGSN) and gateway GPRS support nodes (GGSN). The GGSN acts as a gateway to packet data networks (PDN), such as the Internet, i.e. from the point of view of an outside network PDN the GGSN acts as a router to a subnetwork. The SGSN serves mobile stations MS attached thereto in its service area, transmits and receives data packets from said mobile stations and monitors the location of mobile stations within its service area. The attachment of an MS to a SGSN refers to the formation of a mobility management context for the MS, this function being called GPRS Attach in the GPRS system. In order for the short message service to be able to be utilized via a GPRS network, an interface Gd is standardized between the SGSN and the SMS-GMSC and the SGSN and the SMS-IWMSC. An MS attached to a GPRS network is able to transmit and receive short messages through the GPRS network via the interface Gd. An active PDP (Packet Data Protocol) context is not needed for transmission and reception of a short message, and so short messages are transmitted in a GPRS network using the signalling of the GPRS network. In a GPRS network, signalling is based on the use of GPRS traffic channels.
However, the problem is that the interface Gd is not obligatory in GPRS networks, and so the GPRS network does not have to support the transmission of short messages. If an interface Gs exists between the SGSN and a mobile switching center (MSC/VLR), a mobile-terminated short message can be relayed from the MSC/VLR to the SGSN and further to the MS. The GPRS standard defines that a GPRS-attached but non-IMSI attached mobile station has to transmit short messages via GPRS channels. This causes problems since the MS does not know if the GPRS network supports the transmission of mobile-originated short messages via the GPRS network. If no Gd interface exists or the interfaces of the SMS-IWMSC are not updated to support a short message from the GPRS network, the transmission of short messages fails from the MS via the GPRS network.